The present invention relates generally to automatic transmissions and, more particularly, to automatic transmissions used in gas turbine engines to convert a turbine input into an output suitable to drive auxiliary equipment such as a generator.
Two-spool gas turbine engines include, in flow series, a low pressure compressor, a high pressure compressor, a combustor, a high pressure turbine, and a low pressure turbine. The low pressure compressor is interconnected to the low pressure turbine via a first shaft and forms a low pressure spool. Similarly, the high pressure compressor is interconnected to the high pressure turbine via a second shaft that is concentric with the first shaft to form a high pressure spool. During operation, the gas turbine engine ingests air through an inlet and uses alternating rows of rotating blades and stationary vanes in the low and high pressure compressors to compress the air passing from the inlet into the combustor. Within the combustor, the compressed air mixes with injected fuel to create an air-fuel mixture, which is combusted. The combustion process produces a compressed and heated exhaust flow, which is expanded across alternating rows of rotating blades and stationary vanes to extract work from the exhaust flow. The extracted work drives the low pressure and high pressure compressors via the first and second shafts, respectively. In addition to driving the compressors of the gas turbine engine, the work extracted by the turbines can be used to drive other loads. For example, gas turbine engines can be used to drive a generator in power-producing applications. Furthermore, aircraft use gas turbine engines to drive a fan that generates thrust for propelling the aircraft. In rotor-wing aircraft, the gas turbine engines are used to drive a main rotor and auxiliary rotor in order to propel and control the rotor-wing aircraft.
In many of these applications, and particularly for gas turbine engines used on aircraft, the gas turbine engine drives an auxiliary generator. Electric power produced by the auxiliary generator is used to power various electrical systems on the aircraft. Typically, the auxiliary generators are coupled to a continuously variable transmission to form an integrated drive generator or IDG, which convert the variable speed output from the gas turbine engine to a relatively constant input for driving the generator. In other arrangements, planetary gear systems may be used to couple the auxiliary generator to a shaft of the gas turbine engine. However, each of these arrangements often require additional gear boxes and/or speed reducer arrangements to work in concert with the continuously variable transmission or planetary gear arrangements to achieve the desired speed homogenization of the gas turbine engine shaft. Furthermore, the low pressure spool of a gas turbine engine often experiences greater speed ranges and momentary speed exertions as compared to the high pressure spool.
Therefore, a need exists to provide a less complex, more reliable transmission configured to convert a highly variable input speed range to a relatively narrow output speed range.